Pneumatic Tire

ABSTRACT

A pneumatic tire comprises a tread portion; four main grooves extending in a tire circumferential direction in a tread surface of the tread portion, each having a wave-like shape with periodic oscillation; a center land portion, middle land portions adjacent to the center land portion on either side in a tire lateral direction, and shoulder land portions outwardly adjacent to the middle land portions in the tire lateral direction formed by the main grooves; a plurality of lug grooves that intersect the tire circumferential direction disposed in a row in the tire circumferential direction in the land portions, the plurality of lug grooves each being disposed on a smooth, continuous curved line that crosses the land portions between the outer ends of the tread portion in the tire lateral direction.

TECHNICAL FIELD

The present technology relates to a pneumatic tire that can provideenhanced wear resistance performance while maintaining brakingperformance on wet road surfaces.

BACKGROUND ART

The conventional pneumatic tire described in Japanese Unexamined PatentApplication Publication No. 2014-076764, for example, is designed toimprove both wet performance (braking performance on wet road surfaces)and noise performance (anti-external noise performance). This pneumatictire includes a plurality of wave-shaped circumferential groovesextending in the tire circumferential direction with left and rightgroove walls having a wave-like shape with a wavelength and anamplitude, and at least one row of wave-shaped land portions defined byadjacent wave-shaped circumferential grooves. The shape of the left andright groove walls of the wave-shaped circumferential grooves haveidentical wavelengths but with a phase difference. The groove wall onthe wave-shaped land portion side of one of the left and rightwave-shaped circumferential grooves that define the row of wave-shapedland portions has an amplitude that is greater than that of the groovewall on the wave-shaped land portion side of the other wave-shapedcircumferential groove.

The conventional heavy duty pneumatic tire described in JapaneseUnexamined Patent Application Publication No. S61-175104, for example,is designed to improve both wet performance (braking performance on wetroad surfaces) and uneven wear resistance performance. This heavy dutypneumatic tire includes a tread that includes at least three maingrooves extending in the tire circumferential direction in a zigzagmanner that define the tread in the tire lateral direction, shoulderribs located at least one the outermost sides in the tire lateraldirection, and second ribs inwardly adjacent to the shoulder ribs thatdivide the main grooves. The ridge lines of the shoulder ribs and thesecond ribs that face the main grooves located outward in the tirelateral direction have a smaller zigzag pitch and amplitude.

In the pneumatic tire of Japanese Unexamined Patent ApplicationPublication No. 2014-076764 described above, the wave-like shape of theleft and right groove walls of the wave-shaped circumferential groovesprovide improved braking performance on wet road surfaces. However,improving the rigidity of the land portions to enhance wear resistanceperformance may decrease the braking performance on wet road surfaces.In the heavy duty pneumatic tire of Japanese Unexamined PatentApplication Publication No. S61-175104 described above, the ridge linesof the shoulder ribs and the second ribs that face the main grooveslocated outward in the tire lateral direction have a smaller zigzagpitch and amplitude. The resulting difference in rigidity may adverselyaffect uneven wear. Additionally, the corner portions formed by thezigzag shape of the main grooves may experience uneven wear.

SUMMARY

The present technology provides a pneumatic tire that can provideenhanced wear resistance performance while maintaining brakingperformance on wet road surfaces.

A pneumatic tire comprises:

a tread portion;

four main grooves extending in a tire circumferential direction in atread surface of the tread portion, each having a wave-like shape withperiodic oscillation;

a center land portion, middle land portions adjacent to the center landportion on either side in a tire lateral direction, and shoulder landportions outwardly adjacent to the middle land portions in the tirelateral direction formed by the main grooves;

a plurality of lug grooves that intersect the tire circumferentialdirection disposed in a row in the tire circumferential direction in theland portions, the plurality of lug grooves each being disposed on asmooth, continuous curved line that crosses the land portions betweenthe outer ends of the tread portion in the tire lateral direction.

According to the pneumatic tire, the main grooves have a shape withperiodic oscillation. This increases the overall width of the maingrooves to provide good drainage properties, and allows brakingperformance on wet road surfaces to be maintained. Additionally,according to the pneumatic tire, the lug grooves are disposed on thesmooth, continuous curved line that crosses the land portions betweenthe outer ends of the tread portion in the tire lateral direction. Thisallows good drainage properties to be provided between the landportions, and braking performance on wet road surfaces to be maintained.Furthermore, the lug grooves are disposed on the smooth, continuouscurved line that crosses the land portions between the outer ends of thetread portion in the tire lateral direction. This allows an excessivedifference in rigidity between the land portions in the tire lateraldirection to be suppressed. Thus, wear resistance performance can beimproved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein, the plurality of lug grooves disposedon the curved line communicate with the main grooves at both ends.

According to the pneumatic tire, better drainage properties is providedbetween the land portions, and braking performance on wet road surfacescan be improved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein,

a vehicle inner/outer side orientation when the pneumatic tire ismounted on a vehicle is designated;

the plurality of lug grooves comprise a plurality of through lug groovesdisposed in the tire circumferential direction that continuously passthrough the center land portion and the middle land portion on thevehicle outer side; and

the plurality of through lug grooves each opening to the main groove onthe vehicle outer side of the middle land portion on the vehicle outerside at a first end, passing through the main groove on the vehicleinner side of the center land portion, and terminating within the middleland portion on the vehicle inner side at a second end.

According to the pneumatic tire, the through lug grooves are disposedrunning continuously through the center land portion and the middle landportion on the vehicle outer side. This connects the center main groovesand the main grooves on the vehicle outer side. As a result, gooddrainage properties can be provided, and braking performance on wet roadsurfaces can be improved. Furthermore, the through lug groove terminateswithin the middle land portion on the vehicle inner side. This allows adecrease in rigidity of the middle land portion on the vehicle innerside to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein,

a shoulder land portion narrow groove that intersects the tirecircumferential direction is disposed in the shoulder land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction, the shoulder land portion narrow groovecommunicating with the main groove located inward of the shoulder landportion in the tire lateral direction at a first end and terminatingwithin the shoulder land portion at a second end;

a middle land portion narrow groove that intersects the tirecircumferential direction is disposed in the middle land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction, the middle land portion narrow groovecommunicating with one of the main grooves at the middle land portion ata first end and terminating within the middle land portion at a secondend without reaching the other main groove at the middle land portion;and

a center land portion narrow groove that intersects the tirecircumferential direction is disposed in the center land portion betweena pair of the plurality of lug grooves adjacent in the tirecircumferential direction, the center land portion narrow groovecommunicating with one of the main grooves at the center land portion ata first end and terminating within the center land portion at a secondend without reaching the other main groove at the center land portion.

According to the pneumatic tire, the narrow grooves are disposed in therespective land portions, and communicate with a main groove at thefirst end and terminate within the corresponding land portion at thesecond end. This allows good drainage properties to be provided, andallows a decrease in rigidity of the land portions to be suppressed andbraking performance on wet road surfaces be maintained. Thus, wearresistance performance can be improved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein,

a vehicle inner/outer side orientation when the pneumatic tire ismounted on a vehicle is designated;

a middle land portion narrow groove that intersects the tirecircumferential direction is disposed in the middle land portions, themiddle land portion narrow groove communicating with one of the maingrooves at the middle land portion at a first end and terminating withinthe middle land portion at a second end without reaching the other maingroove at the middle land portion;

a center land portion narrow groove that intersects the tirecircumferential direction is disposed in the center land portion, thecenter land portion narrow groove communicating with one of the maingrooves at the center land portion at a first end and terminating withinthe center land portion at a second end without reaching the other maingroove at the center land portion; and

a relationship A1<A2<A3 is satisfied, where A1 is a ratio between alateral dimension of the middle land portion on the vehicle inner sideand a lateral dimension of the middle land portion narrow groovesdisposed in the middle land portion on the vehicle inner side, A2 is aratio between a lateral dimension of the center land portion and alateral dimension of the center land portion narrow grooves disposed inthe center land portion, and A3 is a ratio between a lateral dimensionof the middle land portion on the vehicle outer side and a lateraldimension of the middle land portion narrow grooves disposed in themiddle land portion on the vehicle outer side.

According to the pneumatic tire, the ratios between the lateraldimensions of the land portions and the lateral dimensions of the narrowgrooves increase in order from the vehicle inner side to the vehicleouter side. In other words, the lateral dimensions of the narrow groovesare greater relative to the lateral dimension of the corresponding landportion from the vehicle inner side toward the vehicle outer side. As aresult, the narrow grooves on the vehicle inner side, which may includemany grooves to contribute to drainage properties, have smaller lateraldimensions than those on the vehicle outer side. This allows an extremedifference in rigidity between the center land portion and the middleland portions to be suppressed. Thus, wear resistance performance can beimproved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein,

a vehicle inner/outer side orientation when the pneumatic tire ismounted on the vehicle is designated;

a middle land portion narrow groove that intersects the tirecircumferential direction is disposed in the middle land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction;

a center land portion narrow groove that intersects the tirecircumferential direction is disposed in the center land portion betweena pair of the plurality of lug grooves adjacent in the tirecircumferential direction; and

relationships B2<B1 and B2<B3 are satisfied, where B1 is a shortestdistance of the middle land portion narrow grooves to the predeterminedcurved line in the middle land portion on the vehicle inner side, B2 isa shortest distance of the center land portion narrow grooves to thecurved line in the center land portion, and B3 is a shortest distance ofthe middle land portion narrow grooves to the curved line in the middleland portion on the vehicle outer side.

According to the pneumatic tire, the distance of the narrow grooves fromthe lug grooves in the center land portion has a magnitude relationshipopposite to that of the middle land portions on either side. As aresult, an extreme difference in rigidity between the center landportion and the middle land portions can be suppressed. Thus, wearresistance performance can be improved.

A pneumatic tire according to an embodiment of the present technologycan provide enhanced wear resistance performance while maintainingbraking performance on wet road surfaces.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 2 is a plan view of a tread portion of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 3 is an enlarged cross-sectional view of a main groove of apneumatic tire according to an embodiment of the present technology.

FIG. 4 is an enlarged cross-sectional view of a lug groove of apneumatic tire according to an embodiment of the present technology.

FIG. 5 is an enlarged cross-sectional view of a narrow groove of apneumatic tire according to an embodiment of the present technology.

FIG. 6 is an enlarged cross-sectional view of a lug narrow groove of apneumatic tire according to an embodiment of the present technology.

FIG. 7 is a table showing the results of performance tests of pneumatictires according to Examples of the present technology.

DETAILED DESCRIPTION

Embodiments of the present technology are described in detail belowbased on the drawings. However, the present technology is not limited tothese embodiments. Constituents of the embodiments include elements thatcan be easily replaced by those skilled in the art and elementssubstantially the same as the constituents of the embodiments.Furthermore, the modified examples described in the embodiments can becombined as desired within the scope apparent to those skilled in theart.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire accordingto the present embodiment. FIG. 2 is a plan view of a tread portion ofthe pneumatic tire according to the present embodiment. FIG. 3 is anenlarged cross-sectional view of a main groove of the pneumatic tireaccording to the present embodiment. FIG. 4 is an enlargedcross-sectional view of a lug groove of the pneumatic tire according tothe present embodiment. FIG. 5 is an enlarged cross-sectional view of anarrow groove of the pneumatic tire according to the present embodiment.FIG. 6 is an enlarged cross-sectional view of a lug narrow groove of thepneumatic tire according to the present embodiment.

Herein, “tire radial direction” refers to the direction orthogonal tothe rotation axis (not illustrated) of a pneumatic tire 1. “Inward inthe tire radial direction” refers to the direction toward the rotationaxis in the tire radial direction. “Outward in the tire radialdirection” refers to the direction away from the rotation axis in thetire radial direction. “Tire circumferential direction” refers to thecircumferential direction with the rotation axis as the center axis.“Tire lateral direction” refers to the direction parallel with therotation axis. “Inward in the tire lateral direction” refers to thedirection toward a tire equatorial plane (tire equator line) CL in thetire lateral direction. “Outward in the tire lateral direction” refersto the direction away from the tire equatorial plane CL in the tirelateral direction. “Tire equatorial plane CL” refers to the planeorthogonal to the rotation axis of the pneumatic tire 1 that passesthrough the center of the tire width of the pneumatic tire 1. “Tirewidth” is the width in the tire lateral direction between componentslocated outward in the tire lateral direction, or in other words, thedistance between the components that are the most distant from the tireequatorial plane CL in the tire lateral direction. “Tire equator line”refers to the line along the tire circumferential direction of thepneumatic tire 1 that lies on the tire equatorial plane CL. In thepresent embodiment, the tire equator line and the tire equatorial planeare both denoted by reference sign CL.

As illustrated in FIG. 1, the pneumatic tire 1 is mainly used onpassenger vehicles and includes a tread portion 2, shoulder portions 3on opposite sides of the tread portion 2, and sidewall portions 4 andbead portions 5 continuing in that order from the shoulder portions 3.The pneumatic tire 1 also includes a carcass layer 6, a belt layer 7,and a belt reinforcing layer 8.

The tread portion 2 is made of rubber material (tread rubber), isexposed on the outermost side of the pneumatic tire 1 in the tire radialdirection, and the surface thereof constitutes the contour of thepneumatic tire 1. The outer circumferential surface of the tread portion2 is a tread surface 21 that mainly comes into contact with a roadsurface when the tire runs.

The shoulder portions 3 are portions located outward in the tire lateraldirection on both sides of the tread portion 2. Additionally, thesidewall portions 4 are exposed on the outermost sides of the pneumatictire 1 in the tire lateral direction. The bead portions 5 each include abead core 51 and a bead filler 52. The bead core 51 is formed by a beadwire, which is a steel wire, wound into an annular shape. The beadfiller 52 is a rubber material that is disposed in the space formed byan end of the carcass layer 6 in the tire lateral direction folded backat the position of the bead core 51.

The end portions of the carcass layer 6 in the tire lateral directionare folded back around the pair of bead cores 51 from inward to outwardin the tire lateral direction, and the carcass layer 6 is stretched in atoroidal shape in the tire circumferential direction to form theframework of the tire. The carcass layer 6 is constituted by a pluralityof coating-rubber-covered carcass cords (not illustrated) disposed inalignment at an angle with respect to the tire circumferential directionthat conforms with the tire meridian direction. The carcass cords aremade of organic fibers (for example, polyester, rayon, and nylon). Atleast one carcass layer 6 is provided.

The belt layer 7 has a multilayer structure in which at least two belts71, 72 are layered. In the tread portion 2, the belt layer 7 is disposedoutward of the carcass layer 6 in the tire radial direction, i.e. on theouter circumference thereof, and covers the carcass layer 6 in the tirecircumferential direction. The belts 71 and 72 each include a pluralityof coating-rubber-covered cords (not illustrated) disposed in alignmentat a predetermined angle with respect to the tire circumferentialdirection (for example, from 20° to 30°). The cords are made of steel ororganic fibers (for example, polyester, rayon, and nylon). Moreover, thebelts 71 and 72 overlap each other and are disposed so that thedirection of the cords of the respective belts intersect each other.

The belt reinforcing layer 8 is disposed outward of the belt layer 7 inthe tire radial direction, i.e. on the outer circumference thereof, andcovers the belt layer 7 in the tire circumferential direction. The beltreinforcing layer 8 includes a plurality of coating-rubber-covered cords(not illustrated) disposed in alignment in the tire lateral directionsubstantially parallel (±5°) with the tire circumferential direction.The cords are made of steel or organic fibers (for example, polyester,rayon, and nylon). The belt reinforcing layer 8 illustrated in FIG. 1 isdisposed so as to cover end portions in the tire lateral direction ofthe belt layer 7. The configuration of the belt reinforcing layer 8 isnot limited to that described above. Although not illustrated in thedrawings, a configuration may be used in which the belt reinforcinglayer 8 is disposed so as to cover the entire belt layer 7.Alternatively, for example, a configuration with two reinforcing layersmay be used, in which the inner reinforcing layer in the tire radialdirection is formed larger than the belt layer 7 in the tire lateraldirection so as to cover the entire the belt layer 7, and the outerreinforcing layer in the tire radial direction is disposed so as to onlycover the end portions of the belt layer 7 in the tire lateraldirection. In another example, a configuration with two reinforcinglayers may be used, in which both of the reinforcing layers are disposedso as to only cover the end portions of the belt layer 7 in the tirelateral direction. In other words, the belt reinforcing layer 8 overlapswith at least the end portions of the belt layer 7 in the tire lateraldirection. Additionally, the belt reinforcing layer 8 is constituted ofa band-like strip material (having, for example, a width of 10 mm) woundin the tire circumferential direction.

For the pneumatic tire 1 according to the present embodiment, thevehicle inner/outer side orientation when the pneumatic tire 1 ismounted on a vehicle is designated. In other words, when the pneumatictire 1 is mounted on a vehicle, the orientation with respect to theinner side and the outer side of the vehicle in the tire lateraldirection is designated. While the designated orientation is notillustrated in the drawings, the orientation is indicated, for example,by an indicator provided on the sidewall portion 4. For the pneumatictire 1, the side facing the inner side of the vehicle when mounted onthe vehicle is referred to as a “vehicle inner side” and a side facingthe outer side of the vehicle is referred to as a “vehicle outer side”.Note that the designations of the vehicle inner side and the vehicleouter side are not limited to cases where the tire 1 is mounted on avehicle. For example, rims have an orientation with respect to the innerside and outer side of the vehicle in the tire lateral direction. Thus,when the pneumatic tire 1 is mounted on a rim, the orientation withrespect to the vehicle inner side and the vehicle outer side in the tirelateral direction is designated.

As illustrated in FIGS. 1 and 2, in the pneumatic tire 1 as describedabove, four main grooves 22 extending in the tire circumferentialdirection are formed in the tread surface 21 of the tread portion 2.

The main grooves 22 include two center main grooves 22A disposedadjacent to the center in the tire lateral direction on either side ofthe tire equatorial plane CL and shoulder main grooves 22B disposedoutward of the center main grooves 22A in the tire lateral direction.Additionally, five land portions 23 are formed by the main grooves 22 inthe tread surface 21. The land portions 23 include a center land portion23A disposed between the center main grooves 22A and on the tireequatorial plane CL; middle land portions 23B disposed between thecenter main grooves 22A and the shoulder main grooves 22B and outwardlyadjacent to the center land portion 23A in the tire lateral direction;and shoulder land portions 23C disposed outward of the shoulder maingrooves 22B in the tire lateral direction, outwardly adjacent to themiddle land portions 23B in the tire lateral direction, and outermost inthe tread portion 2 in the tire lateral direction.

The main grooves 22 (22A, 22B) have a wave-like shape with periodicoscillation and a constant groove width W1 in the tire circumferentialdirection. The wave-like shape of the main grooves 22 can be such that agroove bottom 22 a illustrated in FIG. 3 has a linear shape in the tirecircumferential direction and groove walls 22 b have periodicoscillation such that the groove width W1 is constant in the tirecircumferential direction. Alternatively, the wave-like shape of themain grooves 22 can be such that the groove bottom 22 a and the groovewalls 22 b illustrated in FIG. 3 have periodic oscillation such that thegroove width W1 is constant in the tire circumferential direction. Inthe present embodiment, as illustrated in FIG. 3, the main grooves 22are formed with a chamfer 22 c on the opening edges. The groove width W1of the main grooves 22 is the opening width to the tread surface 21.Thus, the groove width W1 of the main grooves 22 with the chamfer 22 cis the groove width W1 between the outer edges of the chamfers 22 c. Asillustrated in FIG. 3, the center main grooves 22A of the main grooves22 has a groove width W1 ranging from 5 mm to 12 mm and a groove depthD1 ranging from 4 mm to 8 mm. The shoulder main grooves 22B have agroove width W1 ranging from 3 mm to 6 mm and a groove depth D1 rangingfrom 4 mm to 8 mm. The groove width W1 of the center main grooves 22A isgreater than that of the shoulder main grooves 22B. For example, thegroove width W1 of the shoulder main grooves 22B ranges from 10% to 50%of the groove width W1 of the center main grooves 22A. This ispreferable to maintain the drainage properties of the center maingrooves 22A and to ensure the rigidity of the land portions 23 aroundthe shoulder main grooves 22B. Additionally, as illustrated in FIG. 2,the center main grooves 22A of the main grooves 22 have a central line22 d of oscillation located a distance L1 outward from the tireequatorial plane CL in the tire lateral direction, the distance L1 beinga distance ranging from 20% to 30% of a ground contact width TW. Theshoulder main grooves 22B have a central line 22 d of oscillationlocated a distance L2 outward from the tire equatorial plane CL in thetire lateral direction, the distance L2 being a distance ranging from60% to 70% of the ground contact width TW. This is preferable tomaintain the drainage properties of the center main grooves 22A and toensure the rigidity of the land portions 23 around the shoulder maingrooves 22B. The edge shape and dimensions of the land portions 23 inthe tire lateral direction can be determined depending on theoscillation and position in the tire lateral direction of the maingrooves 22.

Herein, “ground contact width TW” refers to the width of the groundcontact region in the tire lateral direction. Additionally, theoutermost edges of the ground contact region in the tire lateraldirection are referred to as ground contact edges T. FIG. 2 illustratesthe ground contact edges T as being continuous in the tirecircumferential direction. The ground contact region is the region wherethe tread surface 21 of the tread portion 2 of the pneumatic tire 1comes into contact with a dry road surface, when the pneumatic tire 1 ismounted on a regular rim, inflated to the regular internal pressure, andloaded with 70% of the regular load. “Regular rim” refers to a “standardrim” defined by the Japan Automobile Tyre Manufacturers Association Inc.(JATMA), a “design rim” defined by the Tire and Rim Association, Inc.(TRA), or a “measuring rim” defined by the European Tyre and RimTechnical Organisation (ETRTO). “Regular internal pressure” refers to“maximum air pressure” defined by JATMA, a maximum value given in “TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or“INFLATION PRESSURES” defined by ETRTO. “Regular load” refers a “maximumload capacity” defined by JATMA, the maximum value given in “TIRE LOADLIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, and a “LOADCAPACITY” defined by ETRTO.

In the pneumatic tire 1 according to the present embodiment, the middleland portion 23B on the vehicle inner side is provided with an auxiliarygroove 24 extending in a linear manner in the tire circumferentialdirection. The auxiliary groove 24 has a narrower groove width than themain groove 22 with the smallest groove width W1. The auxiliary groove24 is centrally disposed between the center main groove 22A and theshoulder main groove 22B that form the middle land portion 23B on thevehicle inner side. The auxiliary groove 24 divides the middle landportion 23B on the vehicle inner side into rib land portions adjacent inthe tire lateral direction. The auxiliary groove 24 has a groove widthranging from 1 mm to less than 3 mm and a groove depth ranging from 4 mmto 8 mm.

In the pneumatic tire 1 according to the present embodiment, the landportions 23 are provided with lug grooves 25 and narrow grooves 26 thatintersect the tire circumferential direction. The lug grooves 25provided in the center land portion 23A are referred to as center landportion lug grooves 25A, the lug grooves 25 provided in the middle landportions 23B are referred to as middle land portion lug grooves 25B, andthe lug grooves 25 provided in the shoulder land portions 23C arereferred to as shoulder land portion lug grooves 25C. The narrow grooves26 provided in the center land portion 23A are referred to as centerland portion narrow grooves 26A, the narrow grooves 26 provided in themiddle land portions 23B are referred to as middle land portion narrowgrooves 26B, and the narrow grooves 26 provided in the shoulder landportions 23C are referred to as shoulder land portion narrow grooves26C. The narrow grooves 26 that communicate with a terminating end ofone of the lug grooves 25 and connect to one of the main grooves 22 orthe auxiliary grooves 24 are referred to as communication narrow grooves26E. Additionally, in the pneumatic tire 1 according to the presentembodiment, a lug narrow groove 27 is provided where both the lug groove25 and the narrow groove 26 are present and connected.

As illustrated in FIG. 4, the lug groove 25 includes groove walls 25 bformed with a chamfer 25 c from the opening portion in the tread surface21 to a groove bottom 25 a. The lug groove 25 has a groove width W2ranging from 2 mm to 4 mm and a groove depth D2 less than that of themain grooves 22 and the auxiliary groove 24 ranging from 2 mm to 6 mm.As illustrated in FIG. 5, the narrow groove 26 includes groove walls 26b formed from the opening portion in the tread surface 21 to a groovebottom 26 a in the tire radial direction. The narrow groove 26 has agroove width W3 ranging from 0.4 mm to 1.0 mm and a groove depth D3 lessthan that of the main grooves 22 and the auxiliary groove 24 rangingfrom 3 mm to 6 mm. As illustrated in FIG. 6, the lug narrow groove 27includes the lug groove 25 and the narrow groove 26 formed in the groovebottom 25 a of the lug groove 25 in the extension direction of the luggroove 25. The sum of the groove depth D2 of the lug groove 25 and thegroove depth D3 of the narrow groove 26 makes an overall groove depth of6 mm or less, less than that of the main grooves 22 and the auxiliarygroove 24. Additionally, the groove depth D3 of the narrow groove 26 ofthe lug narrow groove 27 is preferably 70% or greater of the overallgroove depth (D2+D3) of the lug narrow groove 27 including the luggroove 25.

The center land portion lug grooves 25A provided in the center landportion 23A are disposed in the tire circumferential direction. Thecenter land portion lug grooves 25A communicate at both ends with thecenter main grooves 22A that form the center land portion 23A and dividethe center land portion 23A into a plurality of blocks disposed in a rowin the tire circumferential direction. Note that in the presentembodiment, the center land portion lug grooves 25A are composed overallof the lug narrow grooves 27 where both the lug grooves 25 and thenarrow grooves 26 are present.

The middle land portion lug grooves 25B provided in the middle landportion 23B on the vehicle outer side are disposed in the tirecircumferential direction. The middle land portion lug grooves 25Bcommunicate at both ends with the center main groove 22A and theshoulder main groove 22B that form the middle land portion 23B on thevehicle outer side and divide the middle land portion 23B on the vehicleouter side into a plurality of blocks disposed in a row in the tirecircumferential direction. Additionally, the middle land portion luggrooves 25B provided in the middle land portion 23B on the vehicle outerside communicate at one end with the shoulder main groove 22B that formsthe middle land portion 23B on the vehicle outer side and terminatesthere. Note that in the present embodiment, the middle land portion luggrooves 25B provided in the middle land portion 23B on the vehicle outerside are composed overall of the lug narrow grooves 27 where both thelug grooves 25 and the narrow grooves 26 are present.

The middle land portion lug grooves 25B provided in the middle landportion 23B on the vehicle inner side communicate at the first end withthe center main groove 22A that forms the middle land portions 23B onthe vehicle inner side and terminates at the second end within themiddle land portion 23B on the vehicle inner side without reaching theauxiliary groove 24. Accordingly, the middle land portion 23B on thevehicle inner side is formed as a rib-like land portion. Note that inthe present embodiment, the middle land portion lug grooves 25B providedin the middle land portion 23B on the vehicle inner side are, at theterminating end portion, lug narrow grooves 27 where both the luggrooves 25 and the narrow grooves 26 are present. The communicationnarrow groove 26E extends from the narrow groove 26 of the lug narrowgroove 27 and communicates with the auxiliary groove 24.

The middle land portion lug grooves 25B disposed in the middle landportion 23B on the vehicle outer side and the center land portion luggrooves 25A disposed in the center land portion 23A are disposed suchthat in a plan view they are one groove that passes through the centermain groove 22A on the vehicle outer side, with both ends at the centermain groove 22A between the middle land portion 23B on the vehicle outerside and the center land portion 23A facing one another. The center landportion lug grooves 25A disposed in the center land portion 23A and themiddle land portion lug grooves 25B disposed in the middle land portion23B on the vehicle inner side are disposed such that in a plan view theyare one groove that passes through the center main groove 22A on thevehicle inner side, with both ends at the center main groove 22A betweenthe center land portion 23A and the middle land portion 23B on thevehicle inner side facing one another. Thus, the middle land portion luggroove 25B provided in the middle land portion 23B on the vehicle outerside, the center land portion lug groove 25A provided in the center landportion 23A, and the middle land portion lug groove 25B provided in themiddle land portion 23B on the vehicle inner side constitute one throughlug groove 25E that passes through the center main grooves 22A. In otherwords, a plurality of the through lug grooves 25E are disposed in thetire circumferential direction. The through lug grooves 25E intersectthe tire circumferential direction and continuously pass through thecenter land portion 23A and the middle land portion 23B on the vehicleouter side. Also, the through lug grooves 25E open to the shoulder maingroove 22B on the vehicle outer side of the middle land portion 23B onthe vehicle outer side at the first end, pass through the center maingroove 22A on the vehicle inner side of the center land portion 23A, andterminate within the middle land portion 23B on the vehicle inner sideat the second end without reaching the auxiliary groove 24.

The shoulder land portion lug grooves 25C disposed in each of theshoulder land portions 23C are disposed in a row in the tirecircumferential direction and intersect the tire circumferentialdirection. The shoulder land portion lug grooves 25C open at the firstend to a design end E, which is the outer end of the tread surface 21 ofthe tread portion 2 in the tire lateral direction, and terminate at thesecond end within the shoulder land portion 23C without reaching theshoulder main groove 22B located inward of the shoulder land portion 23Cin the tire lateral direction. Accordingly, the shoulder land portions23C are formed as rib-like land portions. Note that in the presentembodiment, the shoulder land portion lug grooves 25C provided in theshoulder land portions 23C are, at the terminating end portion, lugnarrow grooves 27 where both the lug grooves 25 and the narrow grooves26 are present. The communication narrow groove 26E extends from thenarrow groove 26 of the lug narrow groove 27 and communicates with theshoulder main grooves 22B. Additionally, terminating end portions of theshoulder land portion lug grooves 25C, which are lug narrow grooves 27,are disposed on the ground contact edges T.

Herein, design end E refers to the outermost end of the tread portion 2in the tire lateral direction disposed outward of the ground contactedge T in the tire lateral direction, and is the outermost end of thetread portion 2 in the tire lateral direction where grooves are formed.In FIG. 2, the design end E is illustrated as being continuous in thetire circumferential direction. In other words, in the tread portion 2,when the tire is placed on a dry, flat road surface, the region from theground contact edge T to the design end E is a region which does nottypically come into contact with the ground.

Note that the shoulder land portion lug grooves 25C provided in theshoulder land portions 23C terminate within the shoulder land portions23C and are separated from the through lug grooves 25E described above.However, the first end of the through lug groove 25E, i.e. the end ofthe middle land portion lug groove 25B provided in the middle landportion 23B on the vehicle outer side that communicates with theshoulder main groove 22B, is disposed on an extension of the end portionwhere the shoulder land portion lug groove 25C provided in the shoulderland portion 23C on the vehicle outer side terminates within theshoulder land portion 23C. Additionally, the second end of the throughlug groove 25E, i.e. the end of the middle land portion lug groove 25Bprovided in the middle land portion 23B on the vehicle inner side, isdisposed on an extension of the end portion where the shoulder landportion lug groove 25C provided in the shoulder land portion 23C on thevehicle inner side terminates within the shoulder land portion 23C. Inother words, the lug grooves 25 that include the shoulder land portionlug grooves 25C provided in the shoulder land portions 23C and thethrough lug grooves 25E (the middle land portion lug grooves 25B of themiddle land portion 23B on the vehicle outer side, the center landportion lug grooves 25A of the center land portion 23A, and the middleland portion lug grooves 25B of the middle land portion 23B on thevehicle inner side) are disposed on a smooth, continuous curved line CUthat crosses the land portions 23A, 23B, 23C between the outer ends(design ends E) of the tread portion 2 in the tire lateral direction.Curved line CU refers to a line having only tangent lines with an angleranging from 40° to 90° with respect to the tire lateral direction.

The center land portion narrow grooves 26A of the narrow grooves 26provided in the center land portion 23A are disposed between pairs ofthe center land portion lug grooves 25A adjacent in the tirecircumferential direction and intersect the tire circumferentialdirection. The center land portion narrow grooves 26A communicate withthe center main groove 22A on the vehicle inner side of the center landportion 23A at the first end, and terminate within the center landportion 23A at the second end without reaching the center main groove22A on the vehicle outer side of the center land portion 23A.

The middle land portion narrow grooves 26B provided in the middle landportion 23B on the vehicle outer side are disposed between pairs of themiddle land portion lug grooves 25B adjacent in the tire circumferentialdirection and intersect the tire circumferential direction. The middleland portion narrow grooves 26B communicate with the center main groove22A at the middle land portion 23B at the first end, and terminatewithin the middle land portions 23B at the second end without reachingthe shoulder main groove 22B at the middle land portion 23B.

The middle land portion narrow grooves 26B provided in the middle landportion 23B on the vehicle inner side are disposed between extensions ofpairs of the middle land portion lug grooves 25B adjacent in the tirecircumferential direction and intersect the tire circumferentialdirection. The middle land portion narrow grooves 26B communicate atboth ends with the shoulder main groove 22B at the middle land portion23B and with the auxiliary groove 24. Thus, the middle land portionnarrow grooves 26B provided in the middle land portion 23B on thevehicle inner side divide a portion of the middle land portion 23Bbetween the shoulder main groove 22B and the auxiliary groove 24 into aplurality of blocks disposed in a row in the tire circumferentialdirection.

The shoulder land portion narrow grooves 26C provided in the shoulderland portions 23C are disposed between pairs of the shoulder landportion lug grooves 25C adjacent in the tire circumferential directionand intersect the tire circumferential direction. The shoulder landportion narrow grooves 26C communicate with the shoulder main grooves22B at the first end and terminate at the second end within the shoulderland portions 23C near the outer ends of the tread portion 2 in the tirelateral direction (design ends E), extending beyond the ground contactedges T.

Note that the shoulder land portions 23C are provided with recessedportions 28 near the outer ends of the tread portion 2 in the tirelateral direction (design ends E). The recessed portions 28 have acircular dimple shape and are formed between pairs of the shoulder landportion lug grooves 25C adjacent in the tire circumferential directionin two rows in the tire lateral direction, a laterally inner row 28 awith two recessed portions 28 in the tire circumferential direction anda laterally outer row 28 b with three recessed portions 28 in the tirecircumferential direction. Additionally, the recessed portions 28 of thelaterally outer row 28 b have a larger diameter than those of thelaterally inner row 28 a. The shoulder land portion narrow grooves 26Cprovided in the shoulder land portions 23C terminate at the recessedportions 28 at the second ends. In the present embodiment, the shoulderland portion narrow grooves 26C terminate at the recessed portion 28 ofthe laterally outer row 28 b centrally located in the tirecircumferential direction.

In such a manner, the pneumatic tire 1 according to the presentembodiment is provided with four main grooves 22 in the tread surface 21of the tread portion 2. The main grooves 22 form the center land portion23A, the middle land portions 23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder landportions 23C outwardly adjacent to the middle land portions 23B in thetire lateral direction. The main grooves 22 have a wave-like shape withperiodic oscillation. The lug grooves 25 are disposed in the landportions 23A, 23B, 23C in a row in the tire circumferential directionand intersect the tire circumferential direction. The lug grooves 25 aredisposed on the smooth, continuous curved line CU that crosses the landportions 23A, 23B, 23C between the outer ends of the tread portion 2 inthe tire lateral direction.

According to the pneumatic tire 1, the main grooves 22 have a shape withperiodic oscillation. This increases the overall width of the maingrooves 22 to provide good drainage properties, and allows brakingperformance on wet road surfaces to be maintained. Additionally,according to the pneumatic tire 1, the lug grooves 25 are disposed onthe smooth, continuous curved line CU that crosses the land portions23A, 23B, 23C between the outer ends of the tread portion 2 in the tirelateral direction. This allows good drainage properties to b e providedbetween the land portions 23A, 23B, 23C, and braking performance on wetroad surfaces to be maintained. Furthermore, the lug grooves 25 aredisposed on the smooth, continuous curved line CU that crosses the landportions 23A, 23B, 23C between the outer ends of the tread portion 2 inthe tire lateral direction. This allows an excessive difference inrigidity between the land portions 23A, 23B, 23C in the tire lateraldirection to be suppressed. Thus, wear resistance performance can beimproved.

Preferably, in the pneumatic tire 1 according to the present embodiment,a plurality of the lug grooves 25 on the same curved line CU communicatewith a main groove 22 at both ends.

According to the pneumatic tire 1, better drainage properties isprovided between the land portions 23A, 23B, 23C, and brakingperformance on wet road surfaces can be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the vehicle inner/outer side orientation when the tire is mounted on thevehicle is designated. The lug grooves 25 include the through luggrooves 25E disposed in the tire circumferential direction thatcontinuously pass through the center land portion 23A and the middleland portion 23B on the vehicle outer side. Also, the through luggrooves 25E open to the shoulder main groove 22B on the vehicle outerside of the middle land portion 23B on the vehicle outer side at thefirst end, pass through the center main groove 22A on the vehicle innerside of the center land portion 23A, and terminate within the middleland portion 23B on the vehicle inner side at the second end.

According to the pneumatic tire 1, the through lug grooves 25E aredisposed running continuously through the center land portion 23A andthe middle land portion 23B on the vehicle outer side. This connects thecenter main grooves 22A and the shoulder main grooves 22B on the vehicleouter side. As a result, good drainage properties can be provided, andbraking performance on wet road surfaces can be improved. Furthermore,the through lug groove 25E terminates within the middle land portion 23Bon the vehicle inner side. This allows a decrease in rigidity of themiddle land portion 23B on the vehicle inner side to be suppressed andwear resistance performance to be improved.

Preferably, in the pneumatic tire according to the present embodiment,the shoulder land portions 23C are provided with the shoulder landportion narrow grooves 26C between pairs of the shoulder land portionlug grooves 25C adjacent in the tire circumferential direction thatintersect the tire circumferential direction. The shoulder land portionnarrow grooves 26C communicate with the shoulder main groove 22B inwardof the shoulder land portion 23C in the tire lateral direction at thefirst end and terminate within the shoulder land portion 23C at thesecond end. The middle land portions 23B are provided with the middleland portion narrow grooves 26B between pairs of the middle land portionlug grooves 25B adjacent in the tire circumferential direction thatintersect the tire circumferential direction. The middle land portionnarrow grooves 26B communicate with one of the main grooves 22 (thecenter main groove 22A or the shoulder main groove 22B) at the middleland portion 23B at the first end and terminate within the middle landportion 23B at the second end without reaching the other main groove 22(shoulder main groove 22B or center main groove 22A) at the middle landportion 23B. The center land portion 23A is provided with the centerland portion narrow grooves 26A between pairs of the center land portionlug grooves 25A adjacent in the tire circumferential direction thatintersect the tire circumferential direction. The center land portionnarrow grooves 26A communicate with one of the center main grooves 22Aat the center land portion 23A at the first end and terminate within thecenter land portion 23A at the second end without reaching the othercenter main groove 22A at the center land portion 23A.

According to the pneumatic tire 1, the narrow grooves 26A, 26B, 26C aredisposed in the respective land portions 23A, 23B, 23C, and communicatewith a main groove 22 at the first end and terminate within thecorresponding land portion 23A, 23B, 23C at the second end. This allowsgood drainage properties to be provided, and allows a decrease inrigidity of the land portions 23A, 23B, 23C to be suppressed and brakingperformance on wet road surfaces be maintained. Thus, wear resistanceperformance can be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the vehicle inner/outer side orientation when the tire is mounted on thevehicle is designated; and the middle land portion narrow grooves 26Bthat intersect the tire circumferential direction are disposed in themiddle land portions 23B. The middle land portion narrow grooves 26Bcommunicate with one of the main grooves 22 at the middle land portion23B (the center main groove 22A or the shoulder main groove 22B) at thefirst end and terminate within the middle land portion 23B at the secondend without reaching the other main groove 22 at the middle land portion23B (shoulder main groove 22B or the center main groove 22A). The centerland portion narrow grooves 26A that intersect the tire circumferentialdirection are disposed in the center land portion 23A. The center landportion narrow grooves 26A communicate with one of the center maingrooves 22A at the center land portion 23A at the first end andterminate within the center land portion 23A at the other end withoutreaching the other center main groove 22A at the center land portion23A. The ratios A1, A2, A3 satisfy the relationship A1<A2<A3, where A1is the ratio between a lateral dimension RW1 of the middle land portion23B on the vehicle inner side and a lateral dimension GW1 of the middleland portion narrow grooves 26B provided in the middle land portion 23Bon the vehicle inner side, A2 is the ratio between a lateral dimensionRW2 of the center land portion 23A and a lateral dimension GW2 of thecenter land portion narrow grooves 26A provided in the center landportion 23A, and A3 is a ratio between a lateral dimension RW3 of themiddle land portion 23B on the vehicle outer side and a lateraldimension GW3 of the middle land portion narrow grooves 26B provided inthe middle land portion 23B on the vehicle outer side.

According to the pneumatic tire 1, the ratios between the lateraldimensions of the land portions 23 and the lateral dimensions of thenarrow grooves 26 increase in order from the vehicle inner side to thevehicle outer side. In other words, the lateral dimensions of the narrowgrooves 26 are greater relative to the lateral dimension of thecorresponding land portion 23 from the vehicle inner side toward thevehicle outer side. As a result, the narrow grooves 26 on the vehicleinner side, which may include many grooves to contribute to drainageproperties, have smaller lateral dimensions than those on the vehicleouter side. This allows an extreme difference in rigidity between thecenter land portion 23A and the middle land portions 23B to besuppressed. Thus, wear resistance performance can be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the vehicle inner/outer side orientation when the tire is mounted on thevehicle is designated. The middle land portion narrow grooves 26B thatintersect the tire circumferential direction are disposed in the middleland portions 23B between pairs of the middle land portion lug grooves25B adjacent in the tire circumferential direction. The center landportion narrow grooves 26A that intersect the tire circumferentialdirection are disposed between pairs of the center land portion luggrooves 25A adjacent in the tire circumferential direction. The ratiosB1, B2, B3 satisfy the relationships B2<B1 and B2<B3, where B1 is ashortest distance B1 of the middle land portion narrow grooves 26B tothe predetermined curved line CU in the middle land portion 23B on thevehicle inner side, B2 is a shortest distance of the center land portionnarrow grooves 26A to the curved line CU in the center land portion 23A,and B3 is a shortest distance of the middle land portion narrow grooves26B to the curved line CU in the middle land portion 23B on the vehicleouter side.

According to the pneumatic tire 1, the distance of the narrow grooves 26from the lug grooves 25 in the center land portion 23A has a magnituderelationship opposite to that of the middle land portions 23B on eitherside. As a result, an extreme difference in rigidity between the centerland portion 23A and the middle land portions 23B can be suppressed.Thus, wear resistance performance can be improved.

The pneumatic tire 1 according to the present embodiment is providedwith four main grooves 22 in the tread surface 21 of the tread portion2, each extending in the tire circumferential direction. The maingrooves 22 form the center land portion 23A, the middle land portions23B adjacent to the center land portion 23A on either side in the tirelateral direction, and the shoulder land portions 23C outwardly adjacentto the middle land portions 23B in the tire lateral direction. The maingrooves 22 have a wave-like shape with a constant groove width in thetire circumferential direction and with periodic oscillation. Thevehicle inner/outer side orientation when the pneumatic tire 1 ismounted on a vehicle may be designated.

According to the pneumatic tire 1, the main grooves 22 have a wave-likeshape with periodic oscillation. This increases the overall width of themain grooves 22 to provide good drainage properties, and allows brakingperformance on wet road surfaces to be maintained. Additionally,according to the pneumatic tire 1, the main grooves 22 have a constantgroove width in the tire circumferential direction. This allows therigidity of the land portions 23 (which are formed by the main grooves22) near the main grooves 22 to be made uniform, and wear resistanceperformance to be improved.

Preferably, for the pneumatic tire 1 according to the presentembodiment, the vehicle inner/outer side orientation when the pneumatictire 1 is mounted on a vehicle is designated, and the auxiliary groove24 is provided in the middle land portion 23B on the vehicle inner side,the auxiliary groove 24 having a narrower groove width than the maingrooves 22 and extending in a linear manner in the tire circumferentialdirection.

According to the pneumatic tire 1, the vehicle inner side greatlycontributes to drainage properties, and so by the middle land portion23B on the vehicle inner side being provided with the auxiliary groove24 extending in a linear manner in the tire circumferential direction,good drainage properties can be provided, and thus the brakingperformance on wet road surfaces can be improved. Furthermore, theauxiliary groove 24 has a narrower groove width than the main grooves22. Thus, a decrease in the rigidity of the middle land portion 23B canbe suppressed, and wear resistance performance can be improved.

Preferably, the pneumatic tire 1 according to the present embodimentincludes a plurality of the through lug grooves 25E disposed in the tirecircumferential direction. The through lug grooves 25E intersect thetire circumferential direction and continuously pass through the centerland portion 23A and the middle land portion 23B on the vehicle outerside. Also, the through lug grooves 25E open to the shoulder main groove22B on the vehicle outer side of the middle land portion 23B on thevehicle outer side at the first end, pass through the center main groove22A on the vehicle inner side of the center land portion 23A, andterminate within the middle land portion 23B on the vehicle inner sideat the second end without reaching the auxiliary groove 24.

According to the pneumatic tire 1, the through lug grooves 25E aredisposed running continuously through the center land portion 23A andthe middle land portion 23B on the vehicle outer side. This connects thecenter main grooves 22A and the shoulder main grooves 22B on the vehicleouter side. As a result, good drainage properties can be provided, andbraking performance on wet road surfaces can be improved. Furthermore,the through lug groove 25E terminates within the middle land portion 23Bon the vehicle inner side without reaching the auxiliary groove 24. Thisallows a decrease in rigidity of the middle land portion 23B on thevehicle inner side to be suppressed and wear resistance performance tobe improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the shoulder land portions 23C are provided with the shoulder landportion lug grooves 25C that intersect the tire circumferentialdirection in a row in the tire circumferential direction, the shoulderland portion lug grooves 25C terminating without reaching the shouldermain groove 22B inward of the shoulder land portion 23C in the tirelateral direction.

According to the pneumatic tire 1, the shoulder land portion lug grooves25C provide good drainage properties in the shoulder land portions 23C,and the terminating ends within the shoulder land portion 23C allow adecrease in rigidity of the shoulder land portion 23C to be suppressedand wear resistance performance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the shoulder land portion lug grooves 25C communicate with the shouldermain groove 22B inward of the shoulder land portion 23C in the tirelateral direction via the communication narrow groove 26E, which has anarrower groove width than itself.

Furthermore, according to the pneumatic tire 1, the communication narrowgrooves 26E provide good drainage properties and allow brakingperformance on wet road surfaces to be improved. Additionally, thecommunication narrow groove 26E have a narrower groove width than theshoulder land portion lug grooves 25C. This allows a decrease inrigidity of the shoulder land portions 23C to be suppressed and wearresistance performance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the lug narrow grooves 27 in which the lug grooves 25 and the narrowgrooves 26 are present are disposed between the shoulder land portionlug grooves 25C and the communication narrow grooves 26E.

According to the pneumatic tire 1, the lug narrow grooves 27 aredisposed between the shoulder land portion lug grooves 25C and thecommunication narrow grooves 26E. This allows excessive changes inrigidity at the communicating portion between the shoulder land portionlug grooves 25C and the communication narrow grooves 26E to besuppressed, and wear resistance performance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the shoulder land portion narrow grooves 26C are disposed between pairsof the shoulder land portion lug grooves 25C adjacent in the tirecircumferential direction. The shoulder land portion narrow grooves 26Cintersect the tire circumferential direction and have a narrower groovewidth than the shoulder land portion lug grooves 25C.

According to the pneumatic tire 1, the shoulder land portion narrowgrooves 26C provide good drainage properties and allow brakingperformance on wet road surfaces to be improved. Additionally, theshoulder land portion narrow grooves 26C have a narrower groove widththan the shoulder land portion lug grooves 25C. This allows a decreasein rigidity of the shoulder land portions 23C to be suppressed and wearresistance performance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the shoulder land portions 23C are provided with recessed portions 28 atthe outer ends in the tire lateral direction, and the shoulder landportion narrow grooves 26C terminate at the recessed portions 28 at theouter end portion in the tire lateral direction.

According to the pneumatic tire 1, the outer end portions of theshoulder land portion narrow grooves 26C in the tire lateral directionterminate at the recessed portions 28. This prevents loads acting on theouter end portions of the shoulder land portion narrow grooves 26C inthe tire lateral direction, and allows a decrease in rigidity of theshoulder land portions 23C to be suppressed and wear resistanceperformance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the lug grooves 25 are formed with the chamfers 25 c on the openingportions.

According to the pneumatic tire 1, the lug grooves 25 are formed withthe chamfers 25 c on the opening portions. This allows a decrease inrigidity of the land portions near the lug grooves 25 to be suppressedand wear resistance performance to be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the vehicle inner/outer side orientation when the tire is mounted on thevehicle is designated; and the middle land portion narrow grooves 26Bthat intersect the tire circumferential direction are disposed in themiddle land portion 23B on the vehicle outer side. The middle landportion narrow grooves 26B communicate with the center main groove 22Aon the vehicle inner side of the middle land portion 23B at the firstend and terminate within the middle land portion 23B at the second endwithout reaching the shoulder main groove 22B on the vehicle outer sideof the middle land portion 23B. The center land portion narrow grooves26A that intersect the tire circumferential direction are disposed inthe center land portion 23A. The center land portion narrow grooves 26Acommunicate with the center main groove 22A on the vehicle inner side ofthe center land portion 23A at the first end and terminate within thecenter land portion 23A at the second end without reaching the centermain groove 22A on the vehicle outer side of the center land portion23A.

According to the pneumatic tire 1, the middle land portion narrowgrooves 26B and the center land portion narrow grooves 26A provide gooddrainage properties and allow braking performance on wet road surfacesto be improved. Additionally, by the middle land portion narrow grooves26B and the center land portion narrow grooves 26A terminating withinthe respective land portions 23B, 23A, a decrease in rigidity of theland portions 23B, 23A can be suppressed and wear resistance performancecan be improved.

Preferably, in the pneumatic tire 1 according to the present embodiment,the tread portion 2 has an asymmetrical pattern in the tire lateraldirection, and the difference in groove area ratio between the tworegions on either side of the tire equatorial plane CL in the tirelateral direction is within 2%.

Herein, “groove area ratio” is defined as groove area/(groovearea+ground contact area) expressed as a percentage. “Groove area” isthe total opening area of all of the grooves in the contact patch(ground contact region). Additionally, the groove area and the groundcontact region are the regions measured when the pneumatic tire 1 ismounted on a regular rim, inflated to the regular internal pressure, andloaded with 70% of the regular load.

According to the pneumatic tire 1, the rigidity and the drainageproperties of the land portions located in the two regions on eitherside of the tire equatorial plane CL in the tire lateral direction canbe made uniform, and the effect of enhancing wear resistance performancecan be significantly provided while maintaining braking performance onwet road surfaces. Note that the groove area ratio is preferably higheron the vehicle inner side which contributes more to drainage properties.

Preferably, in the pneumatic tire 1 according to the present embodiment,the recessed portions 28 are formed at the outer ends of the shoulderland portions 23C in the tire lateral direction. The recessed portions28 are formed in two rows in the tire lateral direction, the laterallyinner row 28 a with two recessed portions 28 in the tire circumferentialdirection and the laterally outer row 28 b with three recessed portions28 in the tire circumferential direction. The recessed portions 28 ofthe laterally outer row 28 b have a larger diameter than those of thelaterally inner row 28 a.

According to the pneumatic tire 1, the recessed portions 28 can improvethe appearance of the outer ends of the tread portion 2 in the tirelateral direction. Note that the portion where the recessed portions 28are formed are portions located outward from the ground contact edges Tin the tire lateral direction and do not normally come into contact witha dry road surface. As such, they do not affect the running of thevehicle.

EXAMPLES

In the examples, performance tests for wear resistance performance andbraking performance on wet road surfaces were performed on a pluralityof types of pneumatic tires of different conditions (see FIG. 7).

In these performance tests, pneumatic tires having a tire size of205/55R16 were assembled on 16×6.5J rims, inflated to the regularinternal pressure (200 kPa), and mounted on a test vehicle (1600 cc,front engine front wheel drive sedan passenger vehicle).

Wear resistance performance was evaluated by driving the test vehicledescribed above on a test course with a dry road surface for 5000 km andthen measuring the wear of the land portions via the amount of maingroove remaining. Then, the measurement results were expressed as indexvalues with the value of the Conventional Example being defined as thereference (100). In this evaluation, larger values indicate less wear,which is preferable.

Braking performance on wet road surfaces was evaluated by measuring thebraking distance of the test vehicle from a speed of 100 km/h on a wetroad surface test course with a water depth of 1 mm. Then, themeasurement results were expressed as index values with the value of theConventional Example being defined as the reference (100). In thisevaluation, larger values indicate less braking distance, which ispreferable.

In FIG. 7, the pneumatic tires that were used as the test tires had aconfiguration including five land portions formed by four main grooveson the tread surface, the land portions including the center landportion disposed on the tire equatorial plane CL, the middle landportions disposed adjacent to the center land portion on the two sidesin the tire lateral direction, and the shoulder land portions disposedadjacent to the middle land portions on the outer sides in the tirelateral direction.

The pneumatic tire of the Conventional Example indicated in FIG. 7includes main grooves that oscillate in a wave-like manner.Additionally, in the pneumatic tire of the Conventional Example, the luggrooves of the land portions are disposed off the smooth, continuouscurved line that crosses the land portions between the outer ends of thetread portion in the tire lateral direction.

The pneumatic tires of Examples 1 to 7 include main grooves thatoscillate in a wave-like manner. Additionally, in the pneumatic tires ofExamples 1 to 7, the lug grooves of the land portions are disposed onthe smooth, continuous curved line that crosses the land portionsbetween the outer ends of the tread portion in the tire lateraldirection. The pneumatic tires of Examples 2 to 7 include main grooveswith a constant groove width. In the pneumatic tires of Examples 3 to 7,a plurality of the lug grooves on the same curved line communicate witha main groove at both ends. In the pneumatic tires of Examples 3 to 7,the vehicle inner/outer side orientation when the pneumatic tire ismounted on a vehicle is designated, and a through lug groove isprovided. In the pneumatic tires of Examples 4 to 7, the shoulder landportion narrow grooves of the shoulder land portions communicate withthe main groove at a first end and terminate within the shoulder landportion at the second end, the middle land portion narrow grooves of themiddle land portions communicate with one of the main grooves at thefirst end and terminate within the middle land portion at the secondend, and the center land portion narrow grooves of the center landportion communicate with one of the main grooves at the first end andterminate within the center land portion at the second end. Thepneumatic tires of Examples 5 to 7 have the relationship between lateraldimensions of the land portions and the narrow grooves of A1<A2<A3. Thepneumatic tires of Examples 6 and 7 have the relationships between thedistances of the narrow grooves to the curved line of B2<B1 and B2<B3.In the pneumatic tire of Example 7, the lug grooves of the shoulder landportions do not communicate with the main grooves and terminate withinthe shoulder land portion.

As can be seen from the test results shown in FIG. 7, the pneumatictires of Examples 1 to 7 provided enhanced wear resistance performancewhile maintaining braking performance on wet road surfaces.

1. A pneumatic tire, comprising: a tread portion; four main groovesextending in a tire circumferential direction in a tread surface of thetread portion, each having a wave-like shape with periodic oscillation;a center land portion, middle land portions adjacent to the center landportion on either side in a tire lateral direction, and shoulder landportions outwardly adjacent to the middle land portions in the tirelateral direction formed by the main grooves; and a plurality of luggrooves that intersect the tire circumferential direction disposed in arow in the tire circumferential direction in the land portions, each ofthe plurality of lug grooves being disposed on a smooth, continuouscurved line that crosses the land portions between outer ends of thetread portion in the tire lateral direction.
 2. The pneumatic tireaccording to claim 1, wherein the plurality of lug grooves disposed onthe curved line communicate with the main grooves at both ends.
 3. Thepneumatic tire according to claim 1, wherein a vehicle inner/outer sideorientation when the pneumatic tire is mounted on a vehicle isdesignated; the plurality of lug grooves comprise a plurality of throughlug grooves disposed in the tire circumferential direction thatcontinuously pass through the center land portion and the middle landportion on the vehicle outer side; and the plurality of through luggrooves each opening to the main groove on the vehicle outer side of themiddle land portion on the vehicle outer side at a first end, passingthrough the main groove on the vehicle inner side of the center landportion, and terminating within the middle land portion on the vehicleinner side at a second end.
 4. The pneumatic tire according to claim 1,wherein a shoulder land portion narrow groove that intersects the tirecircumferential direction is disposed in the shoulder land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction, the shoulder land portion narrow groovecommunicating with the main groove located inward of the shoulder landportion in the tire lateral direction at a first end and terminatingwithin the shoulder land portion at a second end; a middle land portionnarrow groove that intersects the tire circumferential direction isdisposed in the middle land portions between a pair of the plurality oflug grooves adjacent in the tire circumferential direction, the middleland portion narrow groove communicating with one of the main grooves atthe middle land portion at a first end and terminating within the middleland portion at a second end without reaching an other main groove atthe middle land portion; and a center land portion narrow groove thatintersects the tire circumferential direction is disposed in the centerland portion between a pair of the plurality of lug grooves adjacent inthe tire circumferential direction, the center land portion narrowgroove communicating with one of the main grooves at the center landportion at a first end and terminating within the center land portion ata second end without reaching the other main groove at the center landportion.
 5. The pneumatic tire according to claim 1, wherein a vehicleinner/outer side orientation when the pneumatic tire is mounted on avehicle is designated; a middle land portion narrow groove thatintersects the tire circumferential direction is disposed in the middleland portions, the middle land portion narrow groove communicating withone of the main grooves at the middle land portion at a first end andterminating within the middle land portion at a second end withoutreaching an other main groove at the middle land portion; a center landportion narrow groove that intersects the tire circumferential directionis disposed in the center land portion, the center land portion narrowgroove communicating with one of the main grooves at the center landportion at a first end and terminating within the center land portion ata second end without reaching the other main groove at the center landportion; and a relationship A1<A2<A3 is satisfied, where A1 is a ratiobetween a lateral dimension of the middle land portion on the vehicleinner side and a lateral dimension of the middle land portion narrowgrooves disposed in the middle land portion on the vehicle inner side,A2 is a ratio between a lateral dimension of the center land portion anda lateral dimension of the center land portion narrow grooves disposedin the center land portion, and A3 is a ratio between a lateraldimension of the middle land portion on the vehicle outer side and alateral dimension of the middle land portion narrow grooves disposed inthe middle land portion on the vehicle outer side.
 6. The pneumatic tireaccording to claim 1, wherein a vehicle inner/outer side orientationwhen the pneumatic tire is mounted on the vehicle is designated; amiddle land portion narrow groove that intersects the tirecircumferential direction is disposed in the middle land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction; a center land portion narrow groove thatintersects the tire circumferential direction is disposed in the centerland portion between a pair of the plurality of lug grooves adjacent inthe tire circumferential direction; and relationships B2<B1 and B2<B3are satisfied, where B1 is a shortest distance of the middle landportion narrow grooves to the curved line in the middle land portion onthe vehicle inner side, B2 is a shortest distance of the center landportion narrow grooves to the curved line in the center land portion,and B3 is a shortest distance of the middle land portion narrow groovesto the curved line in the middle land portion on the vehicle outer side.7. The pneumatic tire according to claim 2, wherein a vehicleinner/outer side orientation when the pneumatic tire is mounted on avehicle is designated; the plurality of lug grooves comprise a pluralityof through lug grooves disposed in the tire circumferential directionthat continuously pass through the center land portion and the middleland portion on the vehicle outer side; and the plurality of through luggrooves each opening to the main groove on the vehicle outer side of themiddle land portion on the vehicle outer side at a first end, passingthrough the main groove on the vehicle inner side of the center landportion, and terminating within the middle land portion on the vehicleinner side at a second end.
 8. The pneumatic tire according to claim 7,wherein a shoulder land portion narrow groove that intersects the tirecircumferential direction is disposed in the shoulder land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction, the shoulder land portion narrow groovecommunicating with the main groove located inward of the shoulder landportion in the tire lateral direction at a first end and terminatingwithin the shoulder land portion at a second end; a middle land portionnarrow groove that intersects the tire circumferential direction isdisposed in the middle land portions between a pair of the plurality oflug grooves adjacent in the tire circumferential direction, the middleland portion narrow groove communicating with one of the main grooves atthe middle land portion at a first end and terminating within the middleland portion at a second end without reaching an other main groove atthe middle land portion; and a center land portion narrow groove thatintersects the tire circumferential direction is disposed in the centerland portion between a pair of the plurality of lug grooves adjacent inthe tire circumferential direction, the center land portion narrowgroove communicating with one of the main grooves at the center landportion at a first end and terminating within the center land portion ata second end without reaching the other main groove at the center landportion.
 9. The pneumatic tire according to claim 8, wherein a vehicleinner/outer side orientation when the pneumatic tire is mounted on avehicle is designated; a middle land portion narrow groove thatintersects the tire circumferential direction is disposed in the middleland portions, the middle land portion narrow groove communicating withone of the main grooves at the middle land portion at a first end andterminating within the middle land portion at a second end withoutreaching the other main groove at the middle land portion; a center landportion narrow groove that intersects the tire circumferential directionis disposed in the center land portion, the center land portion narrowgroove communicating with one of the main grooves at the center landportion at a first end and terminating within the center land portion ata second end without reaching the other main groove at the center landportion; and a relationship A1<A2<A3 is satisfied, where A1 is a ratiobetween a lateral dimension of the middle land portion on the vehicleinner side and a lateral dimension of the middle land portion narrowgrooves disposed in the middle land portion on the vehicle inner side,A2 is a ratio between a lateral dimension of the center land portion anda lateral dimension of the center land portion narrow grooves disposedin the center land portion, and A3 is a ratio between a lateraldimension of the middle land portion on the vehicle outer side and alateral dimension of the middle land portion narrow grooves disposed inthe middle land portion on the vehicle outer side.
 10. The pneumatictire according to claim 9, wherein a vehicle inner/outer sideorientation when the pneumatic tire is mounted on the vehicle isdesignated; a middle land portion narrow groove that intersects the tirecircumferential direction is disposed in the middle land portionsbetween a pair of the plurality of lug grooves adjacent in the tirecircumferential direction; a center land portion narrow groove thatintersects the tire circumferential direction is disposed in the centerland portion between a pair of the plurality of lug grooves adjacent inthe tire circumferential direction; and relationships B2<B1 and B2<B3are satisfied, where B1 is a shortest distance of the middle landportion narrow grooves to the curved line in the middle land portion onthe vehicle inner side, B2 is a shortest distance of the center landportion narrow grooves to the curved line in the center land portion,and B3 is a shortest distance of the middle land portion narrow groovesto the curved line in the middle land portion on the vehicle outer side.